Focus lens structure for an electron gun



Aug. 4, 1970 F. G. 0585 FOCUS LENS STRUCTURE FOR AN ELECTRON GUN Filed Jan. 2. 1968 Maw/a4. 550E064 & 055.:

Anne/val 3,523,205 Patented Aug. 4, 1970 3,523,205 FOCUS LENS STRUCTURE FOR AN ELECTRON GUN Frederick G. Oess, Oceanside, Calif., assignor to Hughes Aircraft Company, Culver City, Calif, a corporation of Delaware Filed Jan. 2, 1968, Ser. No. 694,944 Int. Cl. H01j 29/46, 19/40 US. Cl. 313-85 4 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a focus lens structure of the electrostatic type for use as an integral part of an electron gun.

Of critical importance for the proper operation of an electron gun is the structural configuration of the focus section normally positioned at the forward aspect of the gun. Characteristically, the focus section includes a limiting plate having an aperture therein which defines the electron beam configuration entering the focus section. A focus cylinder assembly is positioned forwardly of the limiting aperture plate and generally concentric with the long axis of the gun. The focus assembly, of course, must be electrically isolated from the cylindrical supporting tube which defines the gun components. For this purpose the supporting structure for the focus cylinder assembly is generally an insulating material, such as ceramic. The entire focus section is conventionally terminated in a final plate having an aperture therein to accommodate exit of the electron beam from the gun. This aperture, of course, is also arranged concentrically with the long axis of the gun.

The electrostatic field created in the focus section importantly afiect the electron beam operation as, for example, in a cathode ray tube it is the focus sections function to properly define the configuration of the electron beam so that the beam will strike the viewing plate with a sharp, clear point focus. It has been found in many prior art focus section structures that isolated electrical charge patterns have developed on exposed ceramic surfaces. As a result of these charge patterns it has been found that the electrostatic field created in the focus section has been penetrated thereby resulting in a deformation of the electron beam from the physical pattern desired to produce optimum focus at the viewing screen.

It is therefore a primary object of the invention to provide a novel structure for an electron gun focus section adapted to provide eflfective focus control.

It is a further object of the invention to provide a novel focus section structure for an electron gun structurally arranged to shield a major segment of the insulating ceramic supporting structure, thereby avoiding excessive isolated charge patterns which could develop on the ceramic, i.e., insulating surfaces.

It is a further object of the invention to provide a focus section structure for an electron gun which will produce an equilibrium charge pattern evenly distributed uniformly around the long axis of the gun and directly related to the potential level of the anode and focus structure.

It is still a further object of the invention to provide a novel focus structure for an electron gun adapted to ease the assembly and fabrication operations.

It is yet another object of the invention to provide a novel focus structure for an electron gun readily adapted to maintain proper component physical relation even when subjected to thermal shock or mechanical shock and vibration.

These and other objects of the invention will become apparent in the course of the following description and from an examination of the related drawings, wherein:

FIG. 1 is a central vertical sectional view of a first embodied focus section of an electron gun; and

FIG. 2 is a view similar to FIG. 1 but illustrating an alternate focus section construction.

Directing attention to the figures it will be understood both FIGS. 1 and 2 show in detail only the focus section of the electron gun which characteristically are at the forward aspect of the gun, the cathode and G1 and G2 electrodes, not being shown, in view of the fact that they are not germane to the present invention and may be of any conventional construction.

Referring to FIG. 1 a metallic cylinder or outer shell is indicated at 10 which houses the electron gun components. A shell 10 is indented at a plurality of points, preferably 3, as at 12, 12, the identations 12 forming a stop for a metallic beam limiting plate or dish 14 which is positioned within the cylinder 10. The indentations 12, therefore, properly locate the beam limiting plate or dish 14 along the longitudinal axis of the gun. The plate 14 is provided with a central aperture 16 known as a limiting aperture in that the size of the opening 16 defines the cross-section of the electron beam that will pass therethrough. To securely position the plate 14 within the cylinder 10 it is desirable to spot-weld its edges as at 18, 18 to the inner wall of the cylinder 10.

A metallic focusing cylinder 20 is carried in concentric relation with the long axis of the cylinder 10 and includes an electrical lead 22 which may be spot-welded to the outer surface of the cylinder 20 and project outwardly of the cylinder 10 via the opening 24 placed in the wall of the latter. The focus cylinder 20 must be electrically isolated from the other components of the electron gun and accordingly is supported from the inner surface of the cylinder 10 by cylindrical ceramic washers 26, 26. The washers 26 are provided with inwardly directed radial lips 28, 28 to which the cylinder 20 is affixed. The outer diameters of the ceramic washers 26 may be lightly pressure fitted within the cylinder 10.

A pair of flared insert cylinders 30, 30 abut the lips 28 of the washers 26, 26 and fit into annular inner cavities formed by the washers. It will be understood, in a preferred mode of fabrication, that the beam limiting aperture plate 14 is first positioned within the cylinder 10 and spot-welded thereto and that the focus cylinder 20", the washers 26, 26 and the flared insert cylinder 30, 30 are subassembled before insertion into the cylinder 10 and then positioned therein as a composite unit. In this connection it will be understood that the opening 24 must be large enough to permit the pasage of the electrical lead 22 during this assembly of the composite unit.

The focus section is completed by the addition of a final aperture dish or end plate 32, the latter having an annular flange 34, which overlies a flared edge 36 formed in the end of cylinder 10. It will be noted that the final apertured dish 32 is formed to provide a clearance Y between the outer diameter of the dish and the inner diameter of cylinder 10. This clearance permits the final aperture dish 32 to be selectively positioned so that its beam passing central aperture 38 may be accurately positioned along the longitudinal axis of the cylinder 10. It will also be noted that the lower flared insert cylinder abuts the limiting aperture dish 14 at the several bosses 31 and that the upper flared insert cylinder 30 abuts the final apertured dish 32 at its bosses 31. In a preferred embodiment of the invention, therefore, the addition of the final aperture dish 32 and its securing via spot-welding at the flare 36 and flange 34 will slightly pressure the entire assembly, thereby assuring longitudinal firmness and integrity of the entire focus section. Passageways 33, 33 are thus provided to accommodate gas passage when the gun is manufactured in, for example, a cathode ray tube.

Persons familiar with electron gun construction will realize that in operation the cylinder 10, being metallic, and being in direct contact with the electron beam accelerating anode (not shown), will therefore have a potential placed thereon equal to the anode potential. Because of the direct metallic contact between the cylinder 10, the limiting aperture dish 14, the lower flared cylinder 30, the upper flared cylinder 30, the final aperture dish 32 and again the cylinder 10, it will be apparent that the flared cylinders 30 will also, in gun operation, exist at anode potential. It will also be apparent that the flared cylinders 30 cover or shield a major segment of the surfaces of ceramic washers 26, thereby preventing isolated electrical charge patterns building up thereon during gun operation.

It will also be noted that the surface of the exposed ceramic lips 28 which separate the flared cylinders 30 from the focus cylinder 20 will have annular uniform charge patterns built up thereon directly related to the potentials applied to the anode (flared cylinders 30) and the focus potential applied to the cylinder 20. As a result of this unique structure, isolated charge patterns are avoided which could undesirably affect the electrostatic field being created which properly focuses the electron beam.

An alternate mode of construction of the focus section of an electron gun is shown in FIG. 2. In FIG. 2 the numeral 100 is used to denote the electron gun supporting cylinder. Again, the cylinder end is flared as at 102. To complete this focus section structure a deeply dished beam limiting aperture plate 104 having limiting aperture 106 centrally thereof is positioned internally of cylinder 100 and spot-welded as at 108, 108 to the internal surface of the cylinder 100. The beam limiting aperture plate 104 is provided with-an annular ledge 110 having several upwardly projecting bosses 111 which engage and support projecting ceramic lips 112 of a lower ceramic washer 114. The lower ceramic washer 114 is internally cavitied to receive a metallic focus cylinder 116, the latter arranged concentrically about the long axis of the cylinder 100. The upper aspect of the focus cylinder 116 is received Within the internal annular cavity of an upper ceramic washer 118, the latter having a forwardly projecting lip 120 which surrounds the central dish 122 of final aperture plate 124. The final aperture plate 124 is provided with an annular shoulder 126 having several downwardly projecting bosses 127 which abut the surface of the upper ceramic washer 118. The final aperture plate 124 may also be spot-welded as at 128, 128 to the flared end 102 of the cylinder 100. Additionally, final aperture plate 124 is provided with a central aperture 130 to accommodate exit of the electron beam. A wire lead 132 is provided and extends through cylinder wall opening 134 to be spot-Welded to the focus cylinder 116 as in the prior embodiment.

It will again be noted that the configuration of the beam limiting aperture plate 104 and the final aperture plate 124 are such as to effectively shield most of the surfaces of ceramic washers 114 and 118, thus preventing unwanted electrical charge patterns being built up thereon as a result of impingement of primary electrons during gun operation. Also, and again as in the earlier embodiment, the limiting aperture plate 104 and the final aperture plate 124 will, during gun operation, exist at anode potential because of their direct metallic connection to the cylinder 100. The cylinder 116, of course, will exist at focus potential and accordingly the ceramic lips 112 and will have a uniform annular charge pattern built up thereon directly related to the anode and focus potential. The uniformity of this pattern, of course, will not affect the electrostatic field being created by the focus potential and optimum beam focusing is assured. It will thus be apparent that the structure of FIG. 2 is an alternate mode of accomplishing the desired electrical advantages described with reference to the first embodiment.

The invention as shown is by way of illustration and not limitation and may be modified in many respects, all within the spirit and scope thereof.

What is claimed is:

1. In a focus lens structure for an electron gun the combination of an annular metallic cylinder, a metallic support plate received within the cylinder and secured to the inner walls thereof, an end plate secured to the end of the cylinder, ceramic washer elements interposed between the plates and abutting the inner surface of the cylinder, a cylindrical focus element carried by the ceramic washer elements and uniformly disposed around the long axis of the cylinder, said plates having central apertures to admit the passage of an electron beam, and means to shield substantial areas of said ceramic elements from straying primary electrons and thereby prevent the buildup of static charges thereon, said ceramic washer elements including surface areas interposed between segments of the plates and the focus element, said plates being adapted to carry anode potential during gun operation, whereby a uniform field gradient is built up on said areas and determined by the potential diflerential between the focus element and the anode potential, said uniform field gradients being in concentric relation with the long axis of the cylinder.

2. A focus lens structure for an electron gun, said focus lens structure comprising:

a metallic cylindrical housing member having a longitudinal axis;

a metallic beam limiting plate internally secured to said cylindrical housing member;

a metallic end plate secured to an end of said cylindrical housing member in opposed relation to said beam limiting plate;

a focussing lens structure situated in said cylindrical housing member about said longitudinal axis and in interposed relation to said beam limiting plate and said end plate;

insulator means for maintaining said focussing lens structure within, and in electrical isolation from, said cylindrical housing member;

an electrical lead operatively coupled to said focussing lens structure; and

shield means for shielding a major portion of the surface area of said insulator means toprevent the buildup of static electrical changes thereon, said shield means including cylindrical members maintained in electrical contact with said beam limiting plate and said end plate whereby said shield means, said beam limiting plate, said end plate and said housing member are maintained at a first electrical potential and said lens structure is maintained at -a second electrical potential.

3. A focus lens structure for an electron gun according to claim 2, and including annular lips, on said insulating means, projecting toward said focussing lens structure and not shielded by said shield means, said lips being shaped as annular insulating areas paralleling said focussing lens structure for providing a uniform electrostatic field gradient about said longitudinal axis.

4. A focus lens structure according to claim 2 wherein said focussing lens structure comprises a cylindrical member having first and second end portions, said end plate and said beam limiting plate respectively being shaped to have a central cup-shaped portion telescopically projecting into said first and second end portion of said cylindrical member.

References Cited UNITED STATES PATENTS 2,449,397 9/ 1948 Lamphere 3133 13 2,840,750 6/1958 White 313313 3,247,410 4/ 1966 Oess 313-82 X 6 3,355,617 11/1967 Schwartz et a1 313313 X 3,376,448 4/1968 Schwartz 313-82 JAMES W. LAWRENCE, Primary Examiner 6 V. LAFRANCHI, Assistant Examiner US. Cl. X.R. 3 133 13 

